2019-03-21T14:17:00ZMicrobial Degradation of Nitrate: Put Microbes to Workhttp://dr.lib.sjp.ac.lk/handle/123456789/8347
Microbial Degradation of Nitrate: Put Microbes to Work
Gunasekara, N.D.; Idroos, F.S; Pathmalal, M.M.
Three nitrate degrading bacteria, namely S1, S2 and S3 strains, were isolated from soil samples collected from agricultural sites at Polonnaruwa, Oruwala and Gampaha, Sri Lanka respectively. Among the isolated strains, S1 showed a maximum nitrate removal rate of 4.20±0.08 mg/L/day whereas S2 and S3 showed nitrate removal rates of 3.45±0.57 mg/L/day and 3.72±0.19 mg/L/day, respectively. The nitrate removal abilities of all three strains were measured at different temperatures (25oC, 30oC, 32oC), different pH (7.0, 7.5, 8.0) and for different nitrate concentrations (15, 30, 45 mg/L) in vitro. The maximum nitrate degrading rate by the bacterium S1 (4.52±0.01 mg/L/day), S2 (4.25±0.47 mg/L/day) and S3 (4.04±0.09 mg/L/day) were detected at 32ºC whereas the highest degradation rate for S1 (4.6±0.05 mg/L/day), S2 (4.38±0.03 mg/L/day) and S3 (4.14±0.25 mg/L/day) bacteria strains was reported when the pH was 8.0. The maximum nitrate degradation was found to be 5.88±0.17, 5.67±0.45 and 5.71±0.43 mg/L/day for S1, S2 and S3 bacteria strains when 45 mg/L of nitrate was present in the medium. A biochemical test tentatively identified the isolates S1, S2 and S3 as Pseudomonas sp., Bacillus sp. and Proteus sp. The bio sand filter developed in co-operating all three bacterial strains showed 6.12±0.06 mg/L/day of nitrate degradation rate within 24 hours.
2019-01-01T00:00:00ZWater quality and microbial contamination status of groundwater in Jaffna Peninsula, Sri Lankahttp://dr.lib.sjp.ac.lk/handle/123456789/7910
Water quality and microbial contamination status of groundwater in Jaffna Peninsula, Sri Lanka
Mahagamage, M.G.Y.L.; Pavithrani, S.Manage; Pathmalal, M. Manage
In Sri Lanka, among 2588 Salmonella positive cases, the highest incidences were recorded from Jaffna peninsula during 2005 to 2013. Therefore, the present study aimed to identify the microbiological and chemical contamination status of groundwater (40 well water) sources in Jaffna during November 2016. The total coliform, E. coli, Salmonella spp. and Shigella spp. along with some physico-chemical parameters of groundwater were studied. The results revealed that entire peninsula was contaminated with total coliform and E. coli bacteria and the parameters recorded were not within the WHO and SLS (Sri Lanka Standards) drinking water quality standards. 38% of sampling locations were positive for Salmonella spp. and among them six sampling locations were being used for drinking purposes. The results of the study correlates with the statistics of typhoid cases recorded in Jaffna. Results of the study also revealed that around 80% of wells were not within the values specified in guidelines of the SLS for drinking water quality on electrical conductivity. Further, 15% of wells recorded greater than 10 mgꞏdm–3 nitrate, which is still below the SLS drinking water standards (45 mgꞏdm–3). According to the water quality data, PCA analysis showed that Jaffna town, Nallur, Tellippalai and Kopay DS divisions has similar characteristics for water quality.
2019-01-01T00:00:00ZDIRECT ORGANOGENESIS OF STEVIA REBAUDIANA IN VITRO USING NODAL EXPLANTShttp://dr.lib.sjp.ac.lk/handle/123456789/7824
DIRECT ORGANOGENESIS OF STEVIA REBAUDIANA IN VITRO USING NODAL EXPLANTS
Gunasena, K.M.; Senarath, S.
Stevia rebaudiana Bertoni is a medicinal herb belonging to the family of Asteraceae. It is a natural sweetener plant, which is estimated to be 300 times sweeter than cane sugar. In this study, reliable protocol was developed for direct organogenesis of S. rebaudiana using in vitro derived nodal explants. Seeds were collected from mother plants and they were surface sterilized. To optimize the surface sterilization procedure, dark color (fertile seeds) seeds were surface sterilized using different concentrations and in different exposure time of carbendazim and sodium hypochlorite (Clorox). Out of different combinations 0.2% carbendazim for 5 minutes, 10% sodium hypochlorite for 10 minutes and 70% ethanol each followed by two successive washings in sterile distilled water was found to be the best for surface sterilization. Two sets of seeds (fresh, stored) were cultured on MS basal medium supplemented with different concentrations of GA3 for seed germination. According to the results seed viability was lost with time and it affected seed germination. Seed germination was not affected by GA3, but seedling height was affected by it. Seeds germinated on MS medium supplemented with 3.0 mg/L GA3 showed the highest seedling height after 10 days. MS basal medium supplemented with different concentrations of BAP and Kin were tested for shoot bud and multiple shoot induction. Out of different media Ms basal medium supplemented with 2.0 mg/L BAP was found to be the best medium for shoot bud and multiple shoot induction within 60 days. Keywords: Stevia rebaudiana, surface sterilization, seed germination, shoot induction, direct organogenesis.
2017-01-01T00:00:00ZBioremediation of Microcystins by Two Native Bacteria: Bacillus Cereus and Rahnella Aquatilishttp://dr.lib.sjp.ac.lk/handle/123456789/7313
Bioremediation of Microcystins by Two Native Bacteria: Bacillus Cereus and Rahnella Aquatilis
Pathmalal, M. Manage; Idroos, F.Sumaiya
Microcystins (MCs) are a group of cyclic heptapeptide hepatotoxins produced by cyanobacteria. Among 70 analogues of MCs, Microcystin-LR (MC-LR) is the dominant type in Sri Lankan water bodies. Contamination of MC-LR in drinking water is a serious health issue. Thus, the present study was carried out to identify freshwater bacteria, which are capable of degrading MC-LR. BIOLOG MT2 plate assay was employed to confirm MC-LR biodegradation by the bacterium Bacillus cereus and Rahnella aquatilis which were isolated from Girandurukotte reservoir and form Ulhitiya reservoir respectively. Classic batch culture experiments showed that B. cereus and R. aquatilis removed 100% of MC-LR at 28oC within 8 and 10 days of incubation respectively. Optimized biodegradation conditions for MC-LR by B. cereus and R. aquatilis were recorded at 320C when phosphates and nitrate concentrations were 0.01ppm and 0.4 ppm respectively in experimental medium. Moreover, B. cereus and R. aquatilis were capable of degrading other MCs analogues; Microcystin-LF (MC-LF), Microcystin –LW (MC-LW), Microcystin –RR (MC-RR) and nodularin (NOD) as well. Molecular studies confirmed that B. cereus and R. aquatilis harbored MC degrading mlrA, mlrB, mlrC and mlrD genes. This is the first record for degradation of MCs and NOD by R. aquatilis.
2018-01-01T00:00:00Z